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Figure 2. MF values at selected time points for right and left side
Graph 1: An illustration of EMG-time graph at 3 rd , 9 th , and 15 th minutes for right back
muscle. “0” shows the starting of the rowing cycle.
DISCUSSION
Decreases in MF and increases in rms-EMG are retained as EMG fatigue indices [1,8].
However, in this study, we observed an increase in rms-EMG without any significant change
in MF. Yeung et al (1999) found that a significant decrease in force generating capacities and
an increase in rms-EMG: Fpeak ratio whereas no significant change was observed in both EMG
amplitude and spectrum parameters after a fatiguing protocol for quadriceps muscles. They
explained observed differences with contractile properties of the muscle [8]. In the present
study, since workload applied during the rowing effort was constant, an increase in EMG
amplitudes without any change occured in frequency characteristics might indicate a decrease
in force generating capacities without detection of early physiological manifestations of
muscle fatigue due to contractile properties of muscle and motor unit recruitment strategies
during sustained contractions. Because, it is well known that increase in EMG amplitude
during fatiguing tasks at submaximal force levels has often been attributed to increase in
motor unit recruitment [9,10]. Fatigue-related loss in force production capacity of working
muscle might be compensated by increased recruitment and, therefore, signal amplitude
increases [9]. On the other hand, we did not observe any significant change in MF values
during rowing effort (Figure 2). Mannion et al. (1996) reported that initial value of MF was